Recombination intermediates of E. coli bacteriophage lambda will be characterized and the recombination enzymes sought. In addition, we shall determine whether the lambda Red system is capable of engaging in reciprocal events. The approach will be to isolate the DNA molecules and study them by electron microscopy. The lambda integration system will be studied in some detail - to understand the peculiar requirements for transcription across the attachment site and the turnoff of DNA synthesis and to isolate the Int protein. The substrates for the DNA packaging system will be studied by examining the products of maturation from linear and circular dimers, trimers, and tetramers of lambda DNA. The use of the electron microscope to map protein binding sites will be developed.